C3 Corvette Fender Flares - Open Wide

Creating Custom Fender Flares For The C3

There is no doubt that as factory delivered our beloved C3 Corvettes have their limitations. This is particularly true when comparisons are made with some of their modern competition. We can certainly lay claim that the C3's gorgeous body lines leave nothing to be desired when making these comparisons, but when comparing some mechanical specifications we can definitely count some disadvantages. Modern sports cars come with the technology of the modern age built in, but as enthusiasts we can often modify our machines to bring the specifications up to those of contemporary cars. Items like aftermarket suspensions, overdrive transmissions, or high performance engines with fuel injection will help bring a C3 up to or even above the standards of most any modern machine.

One area where our cars have a distinct disadvantage that is not so easy to overcome is in tire size. The huge meats of today simply did not exist when our vehicles were conceived, and the body designs were sized to accommodate the tires of the day. For practical purposes, a tire size of 255-60-R15 is about all a stock Corvette can comfortably handle. By upsizing the rim to 17-inch or larger, and optimizing the wheel offset and fit to the inside of the body, tires as wide as 270mm can sometime be accommodated. However, even a 275 is rather narrow compared to what is often seen on today's purpose-build sports cars.

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With available space to the inside fully used up, the only place left to go in seeking wider rubber it to move outwards. While wide rubber is nice to have, a vehicle that is jacked-up with the meats hanging outside the fender line is a poor solution. The requirement if looking to go this route is one well traveled for C3 fans-the fender flare. There are all manner of flares that have been used on the C3 body, from the factory L-88 flares, commonly available as reproductions, to the outlandish Greenwood body kits used in the 1970's. The idea was the same-to create more tire clearance.

We wanted to take advantage of the added clearance of a set of flares for our project '76 Stingray, but we wanted a subtle approach, keeping the original design theme of our car, but in exaggerated form. What this entailed for us was to do as many have done in the past, create a set of custom flares. Our design retained the factory fender lips, and you cannot be more true to the original lines of the car than that. Our custom fender lay-up resulted in an additional 1.25-inches available width, which equates to 37mm of extra tire clearance. Taking a base of 275mm for a fully optimized tire fitment in a stock vehicle, the extra clearance should allow between a 295-305mm tire to be installed, and that is plenty for our purposes.

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C3 Corvette Fender Flares - Open Wide

A few position lines were drawn radially through from the fender lip to the quarter to aid alignment later, and the outer fender was cut along the marked line with a cut-off wheel in an air-powered die grinder.

While making the cuts, it is important to be aware of the double walled and flange-bonded area in the lower wheelhouse. We cut the inner wall flush and then removed the outer wheel lip section.

Since the fender flare will be bonded inside and out, the inner wheelhouse needs to be ground and cleaned so any fiberglass work in here will adhere. We cleaned to an area of about three inches all around the inside of the cut to bare fiberglass.

A set of five steel brackets were formed to bolt the wheel lip back in at a new location, spaced out from the original position. The lip was moved out 1.250-inch at the top center, about .850-inch at the front bottom, and .950-inch at rear bottom. This positioning subtly tips the edge out more at the top center, and allows a gentle sweep off the door edge outward.

The metal brackets were made of thin flat sheet metal, so they can be bent to a curve and screwed through the body at the quarter and the fender lips. The brackets were slotted at the mounting hole to allow adjustment in or out.

A simple wire gage is used to make a line of sight determination of the height of the relocated wheel lip, which can be adjusted by the curve of the mounting brackets. Our final position was just slightly raised from stock (about 1/8-inch). Since the lip is spaced out, the radius of curvature of the lip will no longer meet the quarter, and given the original angle of the lip, the joint needed to go up about as much as out, so a tape line was set at 1.25 up off the quarter cut, and tapering slightly to the sides.

Once the final position was set and locked-down with the brackets, the quarter and wheel lips were cut again. The wheel lip was cut to remove the radiused part, leaving about 1/2-inch, tapering out to just the lip edge at the front. The position was already set with the brackets, since removing this material loses the position reference.

Here we have the quarter after most of the cutting. The area between the lips and the quarters will be fabricated to create the new flared fenders.

To ensure a good bond, the edges of the original fiberglass were roughed with a carbide bit to bare fiberglass.

The next step was to build a mold from the inside. We began with a layer of really heavy-duty and sticky duct tape, tightly laid in strips from the inside.

To add strength and form to the mold, thin cardboard sheets were cut in sections and fitted onto the sticky side of the tape from the top. The mold was made very precisely, using paper patterns for the cardboard to fit together along the joint, edge-to-edge, without overlap, like a puzzle. The ideal was to gain full purchase on the edge when the fiberglass goes in later, and near perfect shape when the'glass cured.

Since the fiberglass will bond to our cardboard mold, it was covered with vinyl tape so that it can be removed once the 'glass cured. The top tape layer tucked a fraction of an inch under the cut edges at the wheel lips and quarter, leaving the cut edge fully exposed.

Next, the fiberglass was laid over the temporary mold; it took about 5-6 layers to equal the thickness of the original material and sit flush, then another layer on top just overlapping both sides a little for strength.

The finished fiberglass work showed a very accurate net shape for our revised fender. After the 'glass cured, the mold and bracing brackets were removed and the seams were overlapped with 'glass from the inside, providing full strength to the bridge section of the flare.

A D/A air sander with #40-grit discs was used to rough-finish to raw fiberglass. We sanded back any high spots until the entire surface was a smooth flowing curve.

A layer of Mar Glass reinforced filler was used next to fill and smooth the flare. It is best to apply the material in one clean continuous wipe.

We worked the Mar Glass with a body file before it reached full hardness. One layer was enough to get the shape nearly perfect.

Once the Mar Glass reached full hardness, the rough filed surface was smoothed by sanding with relatively coarse #40-grit paper on a sanding block.

Reinforced filler like Mar Glass cannot be worked to a perfectly smooth and fine finish. To take our new flare to this level, we gave the entire surface a thin wipe of filler, and block sanded with #80-grit, followed by #180-grit paper.

Once sanded and sprayed with a coat of primer, the new flare looked great. We achieved our goal of retaining the original character of the fender line, while providing for substantially increased tire clearance.

From the front, we were quite pleased with the nice tapered flow of the flare from the door seam out to the fender lip. This is an area where many flare designs can look rather abrupt as the fender line moves outward.